Was the dynamotor fused? If so, has anyone thought to set up a working WE13C transmitter into an appropriate antenna, monitor the current draw on the filament and the plate supplies and then key the mic while changing frequencies, say from from 3105 to 6210? Yes, I am a radio engineer and the thought makes me cringe, too. Would there be a momentary overload as the oscillator and tuning/tank circuits are switched while the plates are energized, enough to exceed the rating of a fuse in the dynamotor circuit? If it was fused, consider the following scenario:

AE indicates she will be switching frequencies from 3105 to 6210 and perhaps either keys the mic by mistake while changing frequencies or continues to hold it down inadvertently after uttering her famous last words. The system overloads, the fuse pops, the transmitter can't transmit. Due to the poor radio communications they've already had with the Itasca, they may have continued "sending" not knowing that they are now no longer being heard. As was mentioned in the other thread, observing an ammeter in either the charging circuit or the via optional RF/final amplifier stage metering if it was so equipped, would be secondary to the fuel gauges. Cockpit noise level and vibration would make it impossible to feel or hear if the dynamotor is running when the mic is keyed. Then as we believe, by luck, skill and a little perspiration, our intrepid duo make it to and land on the reef at Gardner both heaving a huge sigh of relief. Now all they have to do is call for help.....

Since running on only the right-hand engine just enough to charge the batteries would be less noisy, it could be easier to notice the dyanamotor isn't running when the mic is keyed. Or perhaps a post-landing once-over of the radio components prior to calling for help reveals a burned-out fuse. Maybe the missing receive antenna is noticed at this time as well! Either a spare fuse if they had one or scrap of heavy wire would take care of the need and the transmitter is back in operation. Signals are sent, Betty and others take notes, Pan Am says "look here"......but in this scenario it is too bad neither AE or FN receive the electrician-of-the-year award....

Thoughts? Cheers? Jeers? It would be nearly impossible to find "smoking gun" evidence but the basis of this scenario could be tested.

I don't know whether the schematics that have turned up so far answer that question.

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If so, has anyone thought to set up a working WE13C transmitter into an appropriate antenna, monitor the current draw on the filament and the plate supplies and then key the mic while changing frequencies, say from from 3105 to 6210?

I think not.

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Thoughts? Cheers? Jeers? It would be nearly impossible to find "smoking gun" evidence but the basis of this scenario could be tested.

Go for it! Let us know how the experiment turns out.

I am personally content with the thought experiment myself. The fuse blew once; I don't see any reason why it might not have blown again. I don't know how much power there was in the frequency control circuit--it may not have been enough to blow the fuse. We had a long, convoluted of the battery and the dynamotor that I have attempted summarize on the wiki. It sounds to me as though the signal-processing circuits were low power (12 volt) and that the signal from that part of the system was then amplified and broadcast through the high-power circuit. But that's a totally amateur guess.

. . . Would there be a momentary overload as the oscillator and tuning/tank circuits are switched while the plates are energized, enough to exceed the rating of a fuse in the dynamotor circuit? If it was fused, consider the following scenario:

AE indicates she will be switching frequencies from 3105 to 6210 and perhaps either keys the mic by mistake while changing frequencies or continues to hold it down inadvertently after uttering her famous last words. The system overloads, the fuse pops, the transmitter can't transmit.

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. . . keys the mic by mistake while changing frequencies

The dynamotor is enabled when control relay S4 in the 13C transmitter is activated. Activation requires a control input (mic switch closure) and the presence of 12-volt excitation. The 12-volt excitation is applied through a section of the 3-position frequency select switch. This section (D1) provides the excitation only when the switch is centered on one of the three frequency positions. Between positions the excitation is removed and the dynamotor is disabled, so one might expect that the effect (on the dynamotor) of holding the mic switch closed while changing from 3105 kHz to 6210 kHz would be no different from that of a quick open-close sequence of the mic switch. If the latter would pop a dynamotor fuse, then the former might do the same thing.

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. . . continues to hold it down inadvertently after uttering her famous last words.

This scenario, with the mic switch closed but with no modulation applied, is a low load condition for the dynamotor. I don't see it as a fuse-blowing condition.

If a crystal control oscillator coil-condenser combination is tuned too close to its upper limit frequency , oscillation cuts sharply off and no excitation is forwarded to the next driver circuit , or occasionally the power amplifier of a transmitter . A same pnenomenon occurs when in a heterodyne receiver the local oscillator cuts off for the same reason . Refusing to oscillate may be intermittent , i.e. a next time when circuit is operated oscillation resumes . This says that a HF oscillator should always be tuned somewhat below the maximum excitation frequency of the crystal . A phenomenon like this has more probability than a blow-out of the main DC current fuse . Re-establishing a high side detuned oscillator is uncomplicated but it can , on the other hand , nevertheless not be done by non specialists . The phenomenon may explain why from time to time a receiver , resp. transmitter is servicable - unservicable . Main supply fuses in their course are occasionally sensible for the high-drain current when a rotary transformer starts @ low revolution - no repellent voltage . For this class of emergency everybody knows how to manage .

If btw a receiver oscillator , crystal control or not , does not work , the receiver shows completely dead : the operator hears nothing like noise etc. in his phones. Also manually tuned oscillators may suffer cut-off , intermittently or not .

Between positions the excitation is removed and the dynamotor is disabled, so one might expect that the effect (on the dynamotor) of holding the mic switch closed while changing from 3105 kHz to 6210 kHz would be no different from that of a quick open-close sequence of the mic switch.

I looked at the schematic and wondered if the 3-position frequency change switch was a "make-before-break" or a "break-before-make" configuration. Not knowing the type of switch utilized in the transmitter, it seems if it were the "make-before-break" configuration it would result in an extremely noisy and spurious frequency change (not to mention the loading issues!). Probably not the type utilized in the 13C. If it were the "break-before-make" type, a 'clean' switch (from detent to detent without any over- or undershoot) with the key down would indeed cause the dynamotor to spool down for a moment before coming back up as you described. But, from personal experience with other equipment with multi-element switches including higher-power transmitting rigs), I've also experienced uneven movement or element misalignment that could cause contact bouncing resulting in dirty switching. I wonder if this could have been the situation (FN moving into/out of the co-pilot's seat in the cramped cockpit, sudden turbulence, switching dexterity) which may have resulted in a condition rendering the transmitter useless (burned-out dynamotor fuse) yet repairable (post-loss messages). I haven't seen any photos of this transmitter (forgive me if there is one on the site which I've overlooked) so I have to ask if this was a rotary, multi-stack switch or some other configuration?

. . . continues to hold it down inadvertently after uttering her famous last words.

This scenario, with the mic switch closed but with no modulation applied, is a low load condition for the dynamotor. I don't see it as a fuse-blowing condition.

I meant holding the key down after speaking and then moving the switch while continuing to hold the key in, while the former scenario was about if she keyed the mic after the switch was in motion before it came to the next detent (keying in-between positions). At the end of the day, it seems as if the transmitter ceased to function for a period of time (Howland to Gardner) and then was restored to service. A burned-out fuse seems like the most probably candidate and nearly everyone of the time knew fast but not recommended ways to "fix" a burned-out fuse. From a penny behind s screw-in fuse in a residential fuse box to wiring across the fuse receptacle. Something someone with a basic knowledge of radio or electricity would do, especially in a desperate situation.

Too bad we don't have a 13C on hand to test with.......or a breadboarded replica of one with all the modifications as made to the 10E's rig!

I looked at the schematic and wondered if the 3-position frequency change switch was a "make-before-break" or a "break-before-make" configuration.

Friend,

My interpretation of the switching shown in the schematics in Morgan's and Eddy's books is that the operation is break-before-make, but it's the implementation of the D1 switch deck that causes the dynamotor to lose power if the frequency-select switch isn't centered on one of the three frequency positions.

What are you using for a schematic?

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I haven't seen any photos of this transmitter (forgive me if there is one on the site which I've overlooked) so I have to ask if this was a rotary, multi-stack switch or some other configuration?

I have assumed the switch configuration to be of the rotary multi-deck (stack) type, but don't know it for a fact.

I have been unable to find any photos of the 13C transmitter. In a post in the forum archives, Ric indicated having a sales bulletin for the Western Electric 13C transmitter titled A Three-Frequency Radio Transmitter for Airplanes, by W.C. Tinus, Radio Development Department. I've tried to find a copy of it, hoping it might include photographs, but have had no success.

I'm using the unmodified 13C schematic http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/ElectraRadios/Schematic3.jpg which I am having trouble reading on my computer screen (file size/resolution). As it appears to me, the D1 section of the frequency change switch is interesting as it drawn with three larger pads rather than the traditional "dot" indicating the switch contact ("make-before-break" musings). It also shows a traditional dot in-between each of the enlarged contact zones. The 12-volt crystal heater supply is across these larger contacts allowing the switching of 12VDC to the control relay which in part when grounded by pressing the mic switch applies 12 volts to the coil of the dynamotor "start" solenoid. The in-between positions route the 12-volt crystal heater supply to terminal 12 marked only as "signal". I do not know where this connects to including a "destination" on the 20-B receiver schematic (back to the file size resolution issue) http://tighar.org/Projects/Earhart/Archives/Research/ResearchPapers/ElectraRadios/Schematic4.jpg . This is what makes me wonder what would happen given a special switch contact configuration and uneven switch actuation or contact misalignment.

I, too, have been unable to find a photo to confirm the type of switch used. Even though not a perfect "apples to apples" comparison but certainly demonstrating the point, I know later-period the Gonset G-66 amateur band radios not only used a rotary switch to change the tuning and loading circuits but also mechanically rotated a drum with different dial scales for each band selected. http://www.universal-radio.com/catalog/commrxvr/G66B.jpg making tuning on a particular band easier to do. Older units seem to be less "glamourous" (I'm thinking of what I've seen in the radio/navigator position when flying in WW-II vintage bombers) being perhaps a bit difficult to read or operate under certain circumstances. I think this would apply doubly so to novices with their hands full and tanks nearing empty. It would be informative to see what the transmitter and receiver chassis front panels looked like if only to give an idea as to dexterity issues that may have been encountered in basic operation, changing frequencies, reading dial faces, etc.

OK, we're looking at the same schematic, but my look is from the 1939 edition of the book (Aircraft Radio and Electrical Equipment, by H. K. Morgan), which I bought earlier this year.

If my attempt to include an image with this post is successful, it should make clear what's going on with D1. If the switch is rotated CW from the position shown in D1, but not enough to connect the center upper pole to the center lower pole (switch wiper axis vertical), then two conditions exist: 1) the 12-volt connection to S4's coil is lost and 2) 12 volts is connected to SIGNAL. The SIGNAL excitation permits, for example, lighting a lamp to indicate a switch position error--a particularly useful feature for a remotely operated switch.

The action with respect to S4 and enabling/disabling the dynamotor is break-before-make. The break occurs any time the switch is not correctly centered on a frequency position.

I haven't paid much attention to the WE 20B receiver, but Morgan says that it and the 20BA model were designed for remote control, whereas the 20A and 20AA models were designed for direct control at the face of the receiver.

Do we know what the Signal application was used for and for that matter, why a 5-position switch instead of just three? And why "make before break" on the one side of the switch and "break before make" on the other? What would be the need other than an affirmation that the crystal switch was in the proper position using a remote control of the switch (tach head cable). Why not just a 3 position switch to start with? Or did this switch not have detents at each position? Was the signal connection needed for some function within the receiver beyond that provided by the xmit/recv antenna relay? I find this intriguing.....

And why "make before break" on the one side of the switch and "break before make" on the other? What would be the need other than an affirmation that the crystal switch was in the proper position using a remote control of the switch (tach head cable).

I think you just answered your own question, except it wasn't just the status of the crystal portion of the switching that was of interest--it was all of it, D1 having been ganged together with D2 through D8.

Here's what Myron Eddy, in his book Aeronautic Radio, had to say on the matter. On page 303 he wrote "D1 is arranged to prevent energizing S4 unless the frequency-change switches are centered on one of the three operating positions; it also furnishes 12 volts to terminal 12 when it is off-position to operate a remote signal." (I gave an example of what I thought might constitute a remote signal in my previous post.)

So the in-between contact "position" had no detent requiring the need for a verification of the switch position since the tach head cable which operated the actual switch in the chassis could give an ambiguous "feel" to the operation of the switch. That makes sense.

Still I wonder about the cause of the loss of radio reports from near Howland to until on the reef at Gardner. Did something "break" and how/what was it repaired?

So the in-between contact "position" had no detent requiring the need for a verification of the switch position since the tach head cable which operated the actual switch in the chassis could give an ambiguous "feel" to the operation of the switch. That makes sense.

Friend,

I think we're communicating, but I'm not certain of it. The "in-between" contacts provided a means to report a mis-positioned switch.

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